Silviculture of three Millettia tree species from African forests and woodlands

August 31, 2012

Three timber species from different parts of Africa show that the response of species to tree harvesting and the sites of their active regeneration often provide the guidance to effective silvicultural management.

M. stuhlmannii in Miobmo woodland M. stuhlmannii in Mozambique M. grandis used for cattle fences
M. stuhlmannii (Panga-Panga) in moist Miombo woodland, Sofala Province, Mozambique. M. laurentii (Wenge) in tropical moist forest, Equateur Province, Democratic Republic of Congo. M. grandis is used for cattle fences.
M.grandis used for walking sticks M.grandis pods M.grandis seedling
M. grandis is used for decorative walking sticks or kieries. Pods and a seedling in the grassland on the forest margin of M. grandis, similar to those of the other two Millettia species.
Vegetative coppice regrowth Vegetative coppice regrowth stump Vegetative coppice regrowth M. laurentii
Vegetative coppice regrowth on cut stumps of Millettia grandis, M. stuhlmannii and M. laurentii.
M.grandis seedling regeneration Studying M.grandis seedling regeneration M.grandis seedling regeneration on forest margin
Seedling regeneration of Millettia grandis in grassland outside of forest margin, in a forest gap and under a eucalypt belt planted on the forest margin.
Poor stem form of large tree Selective branch pruning of seedling Pruning to produce smaller trees
This poor stem form of a large tree of Millettia grandis could be prevented by selective branch pruning of seedlings and small poles to provide more straight poles and smaller trees.

 

In plantation forestry we apply intensive silvicultural management to provide for productive and sustainable timber resources of good quality. However, resource users from natural forests and woodlands just harvest trees for subsistence and/or commercial benefits without ensuring productive replacement of the harvested trees. Conservation organisations try to abandon harvesting of some tree species that appear to be threatened without trying to develop a basis for sustainable use, with mostly ineffective efforts to control. Is it so difficult to develop even simple but appropriate silvicultural management systems for such species?

Three Millettia species
Millettia in the sub-family Papilionoideae of the legume family Fabaceae has about 150 species in tropical and subtropical regions, with about 90 species in Africa and eight endemic to Madagascar.

M. grandis (Umzimbeet or Msimbithi) occurs on the margins of coastal forest in the Eastern Cape (more commonly) and KwaZulu-Natal, although large trees occur inside the forest. It is commonly used for poles and wood-carving, and the bark is used for traditional medicine and string.

M. stuhlmannii (Panga-panga or Partridge wood) is locally dominant in Miombo woodland in higher rainfall areas and riverine forest in Mozambique and Tanzania and is an important commercial timber species.

M. laurentii (Wenge or African Rosewood) occurs in tropical moist forest in the Congo Basin (Democratic Republic of Congo, Republic of Congo, Cameroon, Gabon and Equatorial Guinea). It is an important commercial timber species (also used for flooring and musical instruments) and is listed as endangered in the IUCN Red List.

All three species have purple to lilac, pea-shaped flowers in upright spikes standing above the leaves, developing into woody, velvety brown pods, which split (often with a loud popping noise) when mature to release flat brown seeds. The wood is generally heavy, hard and strong, with dark brown heartwood and yellow sapwood. Seedlings are easily raised from seed and all three species coppice well. They make well-shaped, shady, decorative garden trees.

Silvicultural management
The response of harvested trees of the three species show us that it actually requires little additional effort to implement silvicultural management to sustain their populations in a state of providing productive resources of good quality. So, how can we improve the sustainable use of these species in their natural environments?

  1. All three species are light-demanding to a greater or lesser degree and therefore some disturbance of forest stands are necessary to ensure their regeneration. For example, Msimbithi does not regenerate from seed under the forest canopy, but does so prolifically in larger forest gaps and on the forest margin. Large trees of this species inside the forest can only have become established in a gap caused by fire spotting, windfalls or earlier resource use.
  2. Selective branch pruning in developing young stands should be applied to improve stem straightness up to a height of the typical pole or log needed. The pruned branches and stems cut from multi-stemmed small trees can be used for firewood and/or laths.
  3. Coppice regrowth on cut stumps should be thinned to provide initially laths, then poles and eventually big trees – a typical coppice management system. The stem of a targeted tree should be cut close to the ground to ensure that the developing coppice stems root into the ground as early as possible. Such coppice regrowth usually grows much faster than seedlings developing from seed.

 

Conclusion and recommendation
Resource users, guided on limited silvicultural intervention, for these and other tree species, have shown that they can see the potential benefits of implementing such sustainable harvesting methods and silvicultural management. The best time to implement silvicultural management would be when resources are being harvested from the current harvesting block. A dedicated small silvicultural field team, as part of the harvesting team, could be tasked to select the stems that could be future crop trees.

Such trees could be selected, marked and harvested by suitable methods to ensure that the remaining growing stock of the population of targeted species could be in a better status during the next harvesting operation (a good balance of regeneration, growing and mature stems of the species).

Published in June 2012

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